Method and apparatus for operating a fuel cell in combination with an electrochemical cell to produce a chemical product

ABSTRACT

A method and apparatus is disclosed for operating a fuel cell 14 which produces electrical energy using hydrogen in combination with a chlorate electrolysis cell which uses electrical energy to produce a chlorate product and hydrogen. A regulator means employs a direct current converter 16 having a gated switch means, such as thyristor 98, to intermittently pass electrical power from the fuel cell to the chlorate electrolysis cell such that the voltage drop across the direct current converter is equal to the difference in voltage between the fuel cell and the electrolysis cell.

CROSS-REFERENCE TO RELATED APPLICATIONS

This is a continuation of application Ser. No. 501,240, filed June 3,1983 which is now abandoned.

DESCRIPTION TECHNICAL FIELD

This invention relates to a method for operating a fuel cell whichproduces electrical energy in combination with an electrochemical cellwhich uses electrical energy. More particularly, this invention isdirected to a method and apparatus for permitting the fuel cell andelectrochemical cell to operate at voltages which are independent ofeach other. This invention has application to all types of fuel cellsincluding acid, base, solid electrolyte and molten carbonate fuel cellsand to all types of electrochemical cells including cells that produce areactant for the fuel cell and cells that do not produce a reactant forthe fuel cell.

BACKGROUND ART

A fuel cell is an electrochemical cell which consumes fuel and anoxidant on a continuous basis to generate electrical energy. The fuel isconsumed at an anode and the oxidant at a cathode. The anode and cathodeare placed in electrochemical communication by an electrolyte. Onetypical fuel cell employs a phosphoric acid electrolyte. The phosphoricacid fuel cell uses air to provide oxygen as an oxidant to the cathodeand uses a hydrogen rich stream to provide hydrogen as a fuel to theanode. After passing through the cell, the depleted air and fuel streamsare vented from the system on a continuous basis.

A typical fuel cell power plant comprises one or more stacks of fuelcells, the cells within each stack being connected electrically inseries to raise the voltage potential of the stack. A stack may beconnected in parallel with other stacks to increase the currentgenerating capability of the power plant. Depending upon the size of thepower plant, a stack of fuel cells may comprise a half dozen cells orless, or as many as several hundred cells. Air and fuel are usually fedto the cells by one or more manifolds per stack. Examples of typicalfuel cell power plants are shown in U.S. Pat. No. 3,585,078 issued toSederquist et al. entitled "Method Of Reformer Fuel Flow Control", U.S.Pat. No. 3,976,507 issued to Bloomfield entitled "Pressurized Fuel CellPower Plant With Single Reacting Gas Stream"; and U.S. Pat. No.4,202,933 issued to Riser, et al. entitled "Method For Reducing FuelCell Output Voltage To Permit Low Power Operation". The informationcontained in these patents is incorporated herein by reference.

Fuel cell components are designed to operate within a band ofpredetermined voltages. Voltages above the predetermined maximum areavoided in acid cells because excessive voltages may damage internalequipment and cause excessively fast corrosion of components such as thecathode. In all fuel cells, such high voltages result in low powerdensities and uneconomical operation of the power plant. Voltages belowa predetermined minimum are avoided because such low voltages adverselyaffect the efficiency of the fuel cell causing the fuel cell to requirea larger amount of fuel for a given amount of power.

As shown in FIG. 2, fuel cells typically produce electrical energy witha voltage characteristic that decreases as current increases. Thisgraphical representation of voltage and current is often referred to asthe voltage characteristic of the fuel cell. The voltage drops withincreasing current because of ohmic and polarization losses. Inaddition, there is a voltage loss with time due to the slowdeterioration of catalysts used at the anode and cathode of the fuelcell.

This decreasing voltage characteristic of fuel cells causes difficultiesin directly coupling the fuel cell to an electrochemical cell to performan electrochemical process. Examples of electrochemical cells that useelectrical energy to produce a chemical product such as chlorine orcaustic alkalis are shown in U.S. Pat. No. 4,031,000 issued to Nakamuraet al. entitled "Diaphragm For Electrolytic Production Of CausticAlkali", in U.S. Pat. No. 4,272,337 issued to Darlington entitled "SolidPolymer Electrolyte Chlor-Alkali Electrolysis Cell" and in U.S. Pat. No.4,273,626 entitled "Electrolyte Series Flow In Electrolytic Chlor-AlkaliCells", the information in which is incorporated herein by reference.

These electrochemical processes typically employ an electrochemical cellhaving a voltage characteristic which is opposite in nature to thevoltage characteristic of the fuel cell. In these cells, the productionof the saleable product is directly proportional to the flow of currentthrough the cells. As shown in FIG. 2, increasing voltages are requiredas the flow of electrical current is increased through theelectochemical cell to produce more product. The increasing voltages areneeded to overcome ohmic and polarization losses in the electrochemicalcell and other losses which are similar to the losses occuring in a fuelcell. Thus, as the current and power consumption is increased in theelectrochemical cell to produce more chemical product at an efficientoperating point, the voltage increases. As the power supplied by thefuel cell increases to meet this demand, the operating voltage of theindividual cells is decreased.

Accordingly, scientists and engineers are seeking a way to match theperformance of a fuel cell to an electrochemical cell to combine the twocells in a cycle and yet to allow the fuel cell to operate at a voltagemost beneficial to the fuel cell and the electrochemical cell to operateat a voltage most beneficial to the electrochemical cell.

DISCLOSURE OF INVENTION

According to the present invention, an electrochemical cell usingelectrical power at a first voltage to produce a chemical product and afuel cell using fuel to produce electrical power at a second voltage arelinked by a device allowing the fuel cell to operate at the secondvoltage and the electrochemical cell to operate at the first voltage.

In accordance with one embodiment of the invention, the electrochemicalcell produces fuel which is consumed in the fuel cell.

In accordance with the present invention, an electrochemical cell isoperated at a first current and a first voltage to produce a chemicalproduct and a fuel cell is operated at a second voltage and a secondcurrent to produce power for the electrochemical cell by converting thepower output of the fuel cell to a current and output voltage whichmatches the voltage of the electrochemical cell.

A primary feature of the present invention is a electrochemical cellwhich uses power to produce a chemical product efficiently at a firstvoltage. Another feature is a fuel cell which utilizes a fuel and anoxidant to produce electrical power efficiently at a second voltage.Another feature is a device for regulating the electrical power receivedfrom the fuel cell. The device is connected to the fuel cell andelectrochemical cell. In one embodiment the electrochemical cell is achlor-alkali cell. In another embodiment the device for regulatingelectrical power includes a direct current converter having a duty cycleto provide for the intermittent flow of current through the directcurrent converter. The converter may be responsive to voltage, (i.e., avoltage regulator) or responsive to current (i.e., a current regulator).

A primary advantage of the present invention is the efficiency whichresults from carrying out an electrochemical process by combining a fuelcell with an electrochemical cell and allowing the fuel cell and theelectrochemical cell to operate at preferred voltages and currentsindependent of each other. In one embodiment, an advantage is theefficient utilization of a by-product of the electrochemical process asfuel in the fuel cell. In one embodiment, an advantage is the reductionin the average cost of electrical power by supplementing electricalpower supplied from an outside source with power provided by the fuelcell.

The foregoing features and advantages of the present invention willbecome more apparent in the light of the following detailed descriptionof the best mode for carrying out the invention and in the accompanyingdrawing.

BRIEF DESCRIPTION OF DRAWINGS

FIG. 1 is a diagrammatic representation of an apparatus for carrying outan electrochemical process, the apparatus including an electrochemicalcell and a fuel cell.

FIG. 2 is a graphical representation of the voltage characteristic of atypical fuel cell and the voltage characteristic of a typicalelectrochemical cell.

FIG. 3 is a diagrammatic representation of the relationship between thefuel cell, the electrochemical cell and regulator means connected to thefuel cell and the electrochemical cell.

FIG. 4 is a schematic illustration of one embodiment of a direct currentconverter used in regulating electrical power between the fuel cell andthe electrochemical cell.

FIG. 5 is a schematic illustration of a second embodiment of a directcurrent converter used in regulating electrical power between the fuelcell and the electrochemical cell.

FIG. 6 is an alternate embodiment of the device shown in FIG. 4.

FIG. 7 is an alternate embodiment of the device shown in FIG. 5.

FIG. 8 is a graphical representation illustrative of wave forms used toexplain the operation of the direct current converter shown in FIG. 4and FIG. 6

FIG. 9 is a graphical representation illustrative of wave forms used toexplain the operation of the direct current converter shown in FIG. 5and FIG. 6. with reference to the wave forms shown in FIG. 8.

BEST MODE FOR CARRYING OUT THE INVENTION

FIG. 1 is a schematic representation of an embodiment of the presentinvention showing an apparatus 10 for carrying out an electrochemicalprocess to produce a chemical product. The apparatus employs achlor-alkali electrochemical electrolysis cell 12 and an electrochemicalfuel cell 14 to produce chlorine and sodium hydroxide. The term fuelcell includes a single fuel cell, a fuel cell stack formed of aplurality of fuel cells, and a fuel cell power plant formed of one ormore fuel cell stacks. Similarly the term electrochemical cell orelectrolysis cell includes a single electrochemical cell, anelectrochemical cell stack formed of a plurality of electrochemicalcells, and an electrochemical plant formed of one or moreelectrochemical stacks.

Regulator means for regulating the power received from the fuel cell 14to adjust the voltage and current of said power and for supplying thepower to the electrolysis cell are connected to the fuel cell and to theelectrolysis cell. An example of such a means is a direct currentregulator 15 having a direct current converter 16 and a control means17. The direct current converter is connected to both the fuel cell andthe electrolysis cell. A high voltage, AC rectifier 18 is in electricalcommunication with a source of purchased electric power. The rectifieris capable of supplying direct current power to the electrolysis cellunder selected operating conditions. Under such operating conditions thefuel cell supplies at least a portion of the power required by theelectrochemical cell.

The fuel cell 14 shown in FIG. 1 is formed of at least one individualfuel cell and in fact is a power plant which includes pluralities offuel cells stacked in series to form fuel cell stacks 20. The fuel cellstacks are connected electrically in parallel to form the power plant.The fuel cell includes a manifold 22 and a manifold 24 for supplyingreactant gases to the fuel cell. A flow path 26 for oxidant rich gasstream, such as air, extends through the manifold 22 and a flow path 28for fuel rich gases, such as a hydrogen rich gas stream, extends throughthe stacks to provide the cathode of each cell with an oxidant and theanode of each cell with fuel. Under normal operating conditions the fuelcell will not consume all of the oxidant in the oxidant stream nor willthe fuel cell consume all of the fuel in the fuel stream.

The electrolysis cell 12 has an anode side 30 and a cathode side 32. Abrine mixer 34 is connected to the anode side via conduit 36. The brinemixer receives sodium chloride via conduit 38 and hot water via conduit40 to form brine. A plurality of chlorine washers 42 are connected tothe anode side by conduit 44. The chlorine washers receive water viaconduit 46 and discharge product chlorine via conduit 48. A stripper 50for the chlorine wash water is connected to the chlorine washers byconduit 52. The stripper discharges clean water for recycling or dumpingvia conduit 54. An on-site steam boiler 56 is in flow communication withthe stripper via conduit 58. The stripper also receives steam from thefuel cell via conduit 60. Alternatively, the conduit 60 might beconnected to other components requiring steam, such as the brine mixer34 or other components requiring heat.

The on-site steam boiler 56 receives fuel via conduit 62 and feed watervia conduit 64. A vacuum evaporator 66 for processing sodium hydroxidereceived from the cathode side of the electrolysis cell via conduit 68also receives high pressure steam from the boiler via conduit 70. Thetemperature of the steam is greater than 300° F. The vacuum evaporatordischarges fifty percent by weight sodium hydroxide via conduit 72. Ahydrogen washer 74 receives hydrogen gas from the cathode side of theelectrolysis cell via conduit 76. The hydrogen discharges water viaconduit 78 and supplies the fuel cell 14 with a hydrogen rich fuelstream via conduit 80. The conduit 80 is connected to the hydrogenmanifold 24 of the fuel cell.

Other electrochemical cells might be used in combination with the fuelcell 14. One example is a chlorate electrolysis cell which uses inputelectrical power to produce a chlorate product and hydrogen. As with thechlor-aklaki process, hydrogen is produced at the cathode and thechlorate product is produced as a result of the electrochemical processat the anode. The product is sent to a reactor for further processing.The hydrogen is preferably processed through a hydrogen washer beforebeing sent to the fuel cell. The chemical reactions are summarized asfollows:

ELECTROLYSIS CELL

    NaCl→Na.sup.+ +cl.sup.-

    Cl.sup.- →1/2Cl.sub.2 +e.sup.- Anode

    1/2Cl.sub.2 +H.sub.2 O+e.sup.- ClO.sup.- +H.sub.2 Cathode

    Na.sup.+ +ClO.sup.- NaOCl

REACTOR

    NaOCl→1/3Na ClO.sub.3 +2/3 NaCl

This electrochemical process was discussed in a paper presented at theInternational Chlorine Symposium 1982 on June 3, 1982 in London, Englandentitled "Energy Saving In Chlorate Production With The Use Of The FuelCell" by I. H. Warren. The paper is available from the ChemeticsInternational Company, a division of C-I-L Inc, 1818 Cornwall Avenue,Vancouver, B.C., Canada, the material in which is hereby incorporated byreference.

Another electrochemical cell having a useful by-product is anelectrolysis cell used in the production of adiponitrile. Thiselectrochemical process was discussed in an article entitled"Adiponitrile" contributed by the Asahi Chemical Industry Co., Ltd. andappearing in the November 1977 issue of Hydrocarbon Processing publishedby the Gulf Publishing Co., U.S.A., the material in which is hereinincorporated by reference. This cell produces oxygen, a by-product. Theoxygen in a combined cycle is sent to the fuel cell for consumption inthe cathode of the fuel cell. Preferably the oxygen will pass through anoxygen washer. In other cells, chlorine may be sent to a fuel cell whichuses chlorine as an oxidant. The by-product of generation of such a fuelis hydrogen chloride.

FIG. 2 is a graphical representation characterizing in general thevoltage characteristic of a typical fuel cell and the voltagecharacteristic of a typical electrochemical process employing anelectrolysis cell. As shown, a fuel cell has a decreasing voltagecharacteristic with current. An electrochemical cell has an increasingvoltage characteristic with current. As discussed earlier, these voltagecharacteristics are not compatible if variations in the operatingcharacteristics of either cell changes, as they most certainly will. Forexample, there is a voltage variation with time for each cell duringoperation because of the natural degeneration of the cells.

FIG. 3 is a diagrammatic representation showing the relationship betweenthe electrolysis cell 12, the fuel cell 14 and the direct currentregulator 15 which is responsive to the output power of the fuel cell.The direct current regulator includes the direct current converter 16and the control means 17. An example of a control means is amicrocomputer having analog to digital signal converters which developsa duty cycle response of two preselected parameters. The control meansdevelops a duty cycle signal for the converter. For example, the dutycycle may be set as a result of a difference between the actual currentI₃ flowing from the regulator in coparison with a desired current ormight be set as a function of the voltage of the electrochemical celland the actual voltage of the fuel cell. As shown in FIG. 8 and FIG. 9,the duty cycle signal may be sent to the regulator in the form of aplurality of energizing gate signals to gated swith means. In addition,the control means has the capability of energizing components in thedirect current converter during start up operations.

FIG. 4 is a schematic illustration of one embodiment of the directcurrent converter 16. This particular direct current converter is abucking regulator which decreases the voltage through the regulator. Thebucking regulator has a first circuit 90 and a second circuit 92. Thesecond circuit is enclosed in broken lines. The first circuit has afirst leg 94 extending between the fuel cell and the electrolysis celland a second leg 96 extending between the fuel cell and electrolysiscell. The first leg includes a first gated switch, such as a firstthyristor 98 responsive to a gate signal Q₁ from the control means 17.The first leg includes an inductor 100 which is connected to the cathodeof the first thyristor and which is in series with the first thyristorbetween the first thyristor and the electrolysis cell. The first leg hasa point A between the first thyristor and the inductor 100. The firstleg includes a means to enable the flow of current to the electrolysiscell through the inductor 100 during the period of time said first gatedswitch is in the nonconducting position and to oppose the divergence ofthe flow of current from the electrolysis cell to ground through point Abetween the first thyristor 98 and the inductor 100. In the embodimentshown, the means is the diode 102; the diode is connected at point Abetween the first thyristor and the inductor in the first leg such thatthe cathode of the diode is joined to the cathode of the first thyristor98. The anode of the diode 102 is connected to the second leg.

The second circuit 92 includes a first leg 106, a second leg 108 and athird leg 110. The first leg has a parallel diode 112 extending inparallel across the first thyristor 98 of the first circuit 90. Theanode of the parallel diode is connected to the cathode of the firstthyristor. A pulse means 114 for creating a current is formed by thesecond leg and the third leg. The second leg extends in parallel acrossthe first thyristor. The second leg has a second gated switch means,such as the second thyristor 116 and a diode 118. The second thyristor116 is responsive to a gate signal Q₂ from the control means 17. Thediode 118 has a cathode connected to the cathode of the first thyristor98. The diode has an anode connected to the second thyristor 116. Thesecond thyristor 116 has an anode connected to the anode of the firstthyristor 98. The third leg is connected in parallel from the anode sideof the first thyristor 98 to the cathode side of the second thyristor116. The third leg includes a capacitor 120 for storing charge and aninductor 122. The capacitor has one side connected to the anode side ofthe first thyristor 98 and a second side connected to the inductor 122and connected through the inductor to the cathode side of the secondthyristor 116.

FIG. 5 is an alternate embodiment of the bucking regulator shown in FIG.4 with two modifications to the second circuit 92. The firstmodification is the substitution of a third gated switch means, such asthe third thyristor 128, for the diode 118. The third thyristor 128 isresponsive to a gate signal Q₃ from the control means 17. The secondmodification is the addition of a resistor 130 which extends from apoint between the capacitor 120 and the inductor 122 in the third leg tothe second leg of the first circuit 96.

FIG. 6 is a schematic illustration of another embodiment of the directcurrent converter 16. This particular direct current converter is aboosting regulator which increases the voltage through the regulator.The boosting regulator has a first circuit 390 and a second circuit 292.The second circuit is enclosed in broken lines. The first circuit has afirst leg 394 extending between the fuel cell and the electrolysis celland a second leg 396 extending between the fuel cell and electrolysiscell. The first leg includes a first gated switch, such as a firstthyristor 298 responsive to a gate signal Q₁ from the control means 17.The first thyristor has an anode connected to the first leg and acathode connected to the second leg. The first leg includes an inductor300 which is connected to the anode of the first thyristor. The firstleg has a point A between the first thyristor 298 and the inductor 300.The inductor 300 is between point A and the fuel cell. The first legincludes a means to enable the flow of current to the electrolysis cellthrough the inductor 300 during the period of time said first gatedswitch is in the nonconducting position and to oppose the divergence ofthe flow of current from the electrolysis cell to ground through point Abetween the first thyristor 298 and the inductor 300. In the embodimentshown, the means to enable and to oppose is a diode 302 having an anodeconnected at point A between the first thyristor and the inductor in thefirst leg and having a cathode connected directly to the electrolysiscell by the first leg. Thus, the diode 302 is between point A and theelectrolysis cell.

The second circuit 292 includes a first leg 306, a second leg 308 and athird leg 310. The first leg has a parallel diode 312 extending inparallel across the first thyristor 298 of the first circuit 390. Theanode of the parallel diode 312 is connected to the cathode of the firstthyristor. A pulse means 314 for creating a current is formed by thesecond leg and the third leg. The second leg extends in parallel acrossthe first thyristor. The second leg has a second gated switch means,such as the second thyristor 316, and a diode 318. The second thyristor316 is responsive to a gate signal Q₂ from the control means 17. Thediode 318 has a cathode connected to the cathode of the first thyristor298. The diode 318 has an anode connected to the cathode of the secondthyristor 316. The second thyristor 316 has an anode connected to theanode of the first thyristor 298. The third leg is connected in parallelfrom the anode side of the first thyristor 298 to cathode side of thesecond thyristor 316. The third leg includes a capacitor 320 for storingcharge and an inductor 322. The capacitor has one side connected to theanode side of the first thyristor 298 and a second side connected to theinductor 322. The second side is also connected through the inductor tothe cathode side of the second thyristor.

FIG. 7 is an alternate embodiment of the boosting regulator shown inFIG. 6 with two modifications to the second circuit 292. The firstmodification is the substitution of a third gated switch means, such asthe third thyristor 328, for the diode 318. The third thyristor isresponsive to a gate signal Q₃ from the control means 17. The secondmodification is the addition of a resistor 330 which extends from apoint between the capacitor 320 and the inductor 322 in the third leg ofthe second circuit to the second leg of the first circuit 396.

Operation of these different embodiments of the regulator is illustratedby the wave forms shown in FIG. 8 and FIG. 9. These wave forms are asimplified representation for clarity of the complex wave forms thatoccur during operation. They are simplified for purposes of explanation.

These wave forms include the Q₁ wave form which is a control wave formgenerated by the control means. The Q₁ wave form is applied to the gateof thyristor 98. If the voltage at the anode is positive with respect tothe cathode, the thyristor Q₁ conducts when the positive voltage Q₁ isapplied gate to cathode. The secondwave form is the voltage changeacross thyristor 98 from the anode to the cathode. The third wave formis the voltage with respect to ground E_(A) at point A in the circuit.The fourth wave form is the current I₉₈ through the first thyristor 98.The wave form I₁₀₀ is the current through the inductor 100 and is ameasure of the current supplied to the electrochemical cell. The waveform I₁₀₂ is the current through the diode 102. The wave form Q₂ is acontrol wave form from the microcomputer and is applied as a positivepulse to the gate of thyristor Q₂. At the time of application, Q₂ is ameasure of the voltage from gate to cathode of the thyristor. The waveform I₁₁₆ is the current flowing through the second thyristor 116. Thevoltage V₁₂₀ is the voltage relative at point C at the side of thecapacitor 20 joined to the anode of the first thyristor and to a measureof the voltage across the capacitor 120. The wave form I₁₁₈ is thecurrent through diode 18. Superimposed on I₁₁₈ is a line showing thecurrent I₁₀₀ flowing at the same point in time through the inductor 100.The current I₁₁₂ is the current through the diode D₁₁₂.

During operation of the apparatus 10, brine is fed from the brine mixervia conduit 36 to the anode side of the electrolysis cell. The chlorine,present as chloride ion in the solution, forms chlorine according to thereaction: 2Cl⁻ →Cl₂ +2_(e). The alkali metal ion and its water ofhydration pass through a permionic membrane to the cathode side 32 ofthe electrochemical cell. The water may be fed both externally into thecathode side or fed as water of hydration passing to the cathode side.The cathodic reaction is H₂ O+e⁻ →OH⁻ +1/2H₂. The chlorine gas evolvedis sent to a chlorine washer via conduit 44 where the chlorine gas ismixed with water to remove contaminants. Wash water discharged from thechlorine washer 52 is flowed to the stripper 50 for chlorine where thewater is mixed with low pressure steam. The overall requirement for fuelfor the process is reduced if low pressure steam is recirculated fromthe fuel cell to transfer heat from the fuel cell to the electricalchemical process. After processing the water discharged from thechlorine washer through the stripper, the cleaned water is dischargedfrom the process. The water may be recycled to the process or dumped.

The on-site steam boiler 56 provides high pressure steam to the vacuumevaporator where sodium hydroxide solution from the cathode is treatedby evaporation. The resultant solution is approximately fifty percent(50%) by weight sodium hydroxide. The hydrogen gas evolved at thecathode is sent to a hydrogen washer which removes containments from thehydrogen gas. The water is discharged from the hydrogen washer and theproduct hydrogen is sent via conduit 80 to the fuel cell 14 forconsumption of at least a portion of the hydrogen in the fuel cell.

In an alternate embodiment, conventional fuel may be treated by a fuelprocessor 82 to provide additional hydrogen to the fuel cell. If enoughhydrogen is provided to the fuel cell the process can dispense with theuse of additional DC power. It is expected that the most efficientoperation of the fuel cell of the overall process will result in themaximum possible consumption of the product hydrogen in the fuel cell toprovide electrical energy to the electrolysis cell and to decrease thereliance of the process on purchased AC electric power from an outsidesource.

The electrochemical cell uses electrical power at a predeterminedvoltage and a predetermined current to produce the chemical product.Depending on the number of electrochemical cells which are groupedtogether and the configuration of the individual cells, thispredetermined voltage and current results in a requirement of a firstvoltage V₁ and a first current I for the electrochemical cell stack.

Each fuel cell utilizes fuel and oxidant to supply electrical power at asecond current and a second voltage. These voltages V₁ and V₂ andcurrents I₁ and I₂ are selected to optimize the performance of theoverall process. Normally the fuel cell will be operated within a bandof voltages which represents the optimum conditions for the individualfuel cell in terms of life, efficiency and economics. For acid fuelcells this band has been found to lies between a lower limit of fiftypercent (50%) of the open circuit voltage and an upper limit which isequal to sixty-five percent (65%) of the open circuit voltage of theindividual fuel cell. Similar ranges have been established for aklalineand molten carbonate fuel cells. Preliminary estimates have establishedthe following ranges: for molten carbonate fuel cells fifty percent(50%) to sixty-five percent (65%) of the open circuit voltage; foralkaline fuel cells the range is equal to seventy percent (70%) toeighty percent of the open circuit voltage. In some situations it may bedesirable for reasons not connected with efficiency or with durabilityof the fuel cell to operate the fuel cell at voltages which aredifferent from the band of predetermined values for the fuel cell or forthe band of balues for the fuel cell which results in the most efficientoperation of the process.

Placing the individual cells in series to form a stack and placing thestacks in parallel to provide additional current results in autilization of fuel and oxidant which produces electrical power at asecond voltage V₂ and a second current I₂. After regulating the directcurrent power by passing the power through the direct current converter,a current I₃ is supplied to the electrochemical cell at voltage V₃ whichmatches the voltage V₁. Purchased electrical power supplied by therectifier at a current I₄ is supplemented by the current I₃ and, undercertain operating conditions, may be replaced entirely by the current I₃resulting in the disconnection of the AC power supply from the circuit.In those cases the current I₃ will equal I₁. Under operating conditionsin which the electrical power is also provided by the rectifier, thecurrent I₁ will be the summation of the current I₃ and I₄.

As shown in FIG. 3, the direct current converter 16 is designed tointermittently pass electrical current. The amplitude of the outputcurrent is the weighted average of the current intermittently flowingthrough the direct current converter. This amplitude is a function ofthe duration of time during which current is allowed to pass through thedirect current converter during any given period of time. The period oftime current flows as a percentage of thegiven period of time is calledthe duty cycle. Thus a fifty percent duty cycle results in the passageof current for fifty percent of any period of time. As discussedearlier, the duty cycle is established in response to input signalswhich establish an error signal. The control means 17 uses these signalsto determine the length of time between a pulse Q₁ turning on the directcurrent converter to allow the direct current converter to pass currentand a pulse Q₂ turns off the direct current converter. The length oftime from the first pulse to the subsequent pulse Q₁ which turns on thecurrent converter is the period of time used to calculate the dutycycle. If the current converter is acting as a voltage regulator, theinput signals will be the output voltage of the current converter andthe desired voltage which may be sent by an operator or automaticallywhich may be automatically established by the system. As a result of theerror signal. A duty cycle is established and the current converter isoperated to provide a variable resistance by intermittently passingcurrent through the regulator. Finally, a duty cycle will be reachedwhich results in a zero error.

Alternatively, and most preferably, the direct current converter acts asa current regulator sensing the output current on the regulator andestablishing an error signal in response to a desired current. Thecontrol means determines the error between the desired current and theactual current establishing a new duty cycle for the current converterand adjusting the duty cycle of the current converter until the correctcurrent as an output is established. The desired current may be set, forexample, to consume all of the hydrogen which is being produced by theelectrochemical cell in which case the microcomputer may sense thehydrogen input to the fuel cell (e.g., signal F) and use a lookup tableto determine the output current of the fuel cell. Then, using thevoltage available from the electrochemical cell the microcomputer willdetermine the current which must be delivered by the converter. Anyincrease in hydrogen output is accompanied by an increase in the amountof current that can be delivered and the concomitant decrease in theelectrical power purchased until the total power going to theelectrolysis cell satisfies the operating requirements of electrolysiscell. In ine embodiment additional hydrogen is produced by processingfuel through a fuel processor such that the maximum current availablefrom the fuel cell to the electrolysis cell satisfies the electrolysiscell so that no additional electrical power need be purchased.

During operation of the buck regulator, the anode side of thyristor 98₁has a voltage which is equal to the voltage supplied by the fuel cellE_(fc). As shown in FIG. 8, during the time thyristor 98 is in the offposition, the anode is positive with respect to the cathode as is shownby the waveform V₉₈. The waveform Q₁ describes the pulses which areplaced on the gate of thyristor 98 and the gate to cathode voltage ofthyristor 98. At time equal zero, the Q₁ waveform or control waveform isa pulse which is a step function having a width of some microseconds.The pulse is applied gate to cathode and causes the thyristor 98 toconduct. The voltage V₉₈ across the thyristor goes to zero because oncethe thyristor is in conduction, the voltage drop across the thyristor isessentially zero. By placing the positive pulse on the gate of thethyristor, a positive voltage from gate to cathode results and thethyristor becomes conducting because the voltage from the anode to thecathode was positive.

At point C on the positive side of the capacitor, the capacitor ischarged up with some positive voltage E_(f) +_(c) which is greater thanthe voltage E_(fc) (E_(f) +_(c) >E_(fc)) The summation of the currentI₉₈ through the first thyristor and the current I₁₀₂ through the diode102 of the first circuit is equal to the current I₁₀₀ supplied throughthe inductor 100 to the load which is the electrolysis cell. Before thethyristor 98 is turned on by the pulse Q₁ at time equal to zero, thecurrent through the thyristor Q₁ is equal to zero (I₉₈ =0, T<0). Thecurrent I₁₀₀ through the load is decreasing from some high valve. Thecurrent I₁₀₂ is equal to the current I₁₀₀. As the thyristor 98 is turnedon, the load current I₁₀₀ starts to increase, the thyristor currentrapidly increases to a value equal to the current through I₁₀₂ and thecurrent through T₁₀₂ goes back to zero. In effect, as thyristor 98 isturned on, the current fed to the electrolysis cell is transferred frombeing fed from the diode 102 to being fed from the thyristor Q₁. Theinductor 100 ensures that the current I₁₀₀ does not changeinstantaneously but rather acts to retard the instantaneous increase incurrent and acts as a means to resist changes in current to theelectrochemical cell. The slopes of the changing currents in thethyristor and the diode are not instantaneous but are nearly so. Thecurves as drawn to approximate a perfect switch having instantaneousresponse, but as will be realized, there is some small slope which hasbeen eliminated for clarity.

Once the thyristor 98 begins conducting, the thyristor 98 will conductuntil the thyristor is made nonconducting. For the thyristor 98 toconduct current intermittently, the thyristor must stop carryingcurrent. Accordingly, a second circuit 92 is provided to turn off thethyristor. This process is referred to as commutation. Commutation isbegun by sending a control waveform Q₂ to the gate of thyristor 116 andcausing a positive voltage to exist between the gate and the cathode.The voltage across the capacitor through the thyristor 116 is positiveand as a result of the control waveform Q₂, a pulse of current I₁₁₆begins to flow as shown in FIG. 8.

The time sclae for these waveforms is very expanded to show theapproximate shape of the waveform. In actual operation these waveformsappear almost as pulses. As the current I₁₁₆ flows to the capacitor 120the voltage V₁₂₀ at point C decreases rapidly from the positive voltageE_(f) +_(c) to a negative voltage -E_(f) +_(c). The components in thesecond circuit such as the diode 118 and the inductor 122 are sized suchthat the capacitor will fully charge in a reverse polarity from thepolarity that existed at a time just before Q₂. Thus, the circuit ringsaround upon itself, fully charging the capacitor before the capacitor120 begins to discharge through the diode 118. As the capacitordischarges, a current I₁₁₈ is generated. I₁₁₈ is the commutation currentis generated.

As the pulse of current I₁₁₈ comes out of the capacitor through diode118 and moves toward point A, the current I₉₈ goes to zero. One waydescribing the commutation is the current flowing from the fuel cell tothe first thyristor 98 seeks to go to point C which is no at -E_(f)+_(c) and does not flow to point A which is at a voltage equal to E_(f)+_(c). Thus, the current I₉₈ is shunted and replaced by a portion of thecurrent I₁₁₈. Alternatively, the process may be described as theproduction of a pulse of current through diode 118 which may go throughdiode 112 or towards point A. The current I₁₀₀ is still building up,and, as the large pulse of current I₁₁₈ approaches point A, the inductorprevents an instantaneous increase in the current. As a result, thecurrent I₉₈ no longer flows, the current I₁₀₀ is replaced by a portionof the current I₁₀₂ and the remainder is passed through diode 112 asI₁₁₂. As can be seen, I₁₁₂ is a very small pulse of current that returnsto charge the capacitor 120 at a voltage E_(f) +_(c). As the pulse ofcurrent I₁₁₈ moves through point A and through diode 112 (with thethyristor Q₁ in a nonconducting position), the diode the first circuitbeings to pass a current I₁₀₂ to supply the current I₁₀₀ to theelectrolysis cell. The magnitudes of I₁₀₂ and I₁₀₀ are equal and thecurrent I₉₈, which was building up at this point in time, now returns tozero. The voltage E_(a) goes back to zero and the voltage across thethyristor goes back to positive. As a result, a negative voltage existsacross the inductor and is equal to minus V load which is the voltagedropped across the electrolysis cell.

In summary, as a current passes through diode 112 during the timecurrent I₁₁₈ is greater than I₁₀₀. The interval when diode 112 conductsand I₉₈ is zero is the commutation time for thyristor 98. As I₁₁₈ dropsto the value of I₁₀₀, diode 112 no longer conducts. Current now flowsfrom fuel cell through the inductor 122, capacitor 120, diode 118 andthe filter reactor to the load.

FIG. 9 summarizes several of the voltages and currents in the firstconduit for the buck and boost regulators. The cycle for the buckregulator T_(c) (T_(c) =T_(cycle)) includes a period T_(on) during whichthe thyristor 98 (switch) is in the "on" position and conducting and aperiod of time T_(off) during which the thyristor 98 is not conducting.Because the cycle time T_(c) is very great compared to the pulse time ittakes for the thyristor to turn off when the pulse Q₂ arrives atthyristor 116, the pulses Q₁ and Q₂ are shown as spikes coinciding withthe on and off period for the thyristor 98. When the thyristor 98 is on,point A has a voltage E_(A) which is equal to the voltage E_(fc)neglecting any small circuit losses that might exist. When the thyristorswitch 98 is off, point A has a voltage E_(A) which is equal to zero(E_(A) =0). The current I₁₀₀ is increasing during the period of time theswitch is on and is decreasing during the period of time the switch 98is off. The current I₁₀₀ is the summation of the current I₉₈ through thethyristor switch and the current I₁₀₂. The current I₁₀₂ is zero duringthe period of time that the thyristor switch 98 is on and is decreasingfrom some preselected value during the period of time when the switch isoff. The current I₉₈ through the thyristor switch 98 is increasingduring the on period and is decreasing from its maximum value during theoff period. As can be seen, the pattern for the current I₁₀₀ is one ofdeveloping a triangular current where the rising portion is beingcarried by the switch 98 and the falling portion is being carried by thediode 102.

The voltage V₁₀₀ across the inductor is equal to the inductancemultiplied by the first derivative of the current with respect to time(V₁₀₀ =I_(nd) ·di/dt). The voltage drop is positive during the period oftime when the switch is on. The voltage drop is equal to the voltage atpoint A minus the voltage across the load. As can be seen, the positivevoltage is less than the voltage supplied by the fuel cell. The voltagedrop V₁₀₀ across the inductor 100 is negative during the period of timewhen the switch is off being equal to the negative of the load voltage.

In summary we have a switch means which is the thyristor 98, a means toresist changes in current through the primary circuit which is theinductor 100 and a means to maintain the current flowing in the means toresist changes in current which is the diode 102. The second circuit 92is a means to turn off the switch means by generating a current pulsethat is greater than the current flowing through the means to resistchanges in current, inductor 100.

The boost regulator works in a similar fashion to the buck regulatorbut, instead of the voltage being lower than the source (the fuel cellvoltage), the voltage is higher as a result of the orientation of thecomponents. The commutation or second circuit 292 for the boostregulator works in the same fashion as the commutation circuit describedabove for the buck regulator.

As with the buck regulator, the pulse signals Q₁ and Q₂ to the firstthyristor switch 298 and the second thyristor switch 318 determine theperiod during which the thyristor 298 conducts and the period duringwhich the thyristor switch 98 does not conduct. The voltage E_(a) atpoint A is pulled to ground (E_(a) =0) during the period of time thethyristor switch 298 is "on" or conducting. The thyristor 298 acts as ashort circuit. The voltage E_(a) at point A is equal to the voltageE_(fc) of the fuel cell source plus the voltage across the inductor V₃₀₀(i.e., E_(a) =E_(fc) +Ind·di/dt). Although the voltage across theinductor 300 is negative during the period when the switch is in the onposition, the voltages E_(A) at point A is zero when you turn the switchon. Thus the voltage across V₃₀₀ is as shown, staring negative when theswitch is on and going positive when the switch is off. The current I₃00 through the inductor 300 increases during the period of time when theswitch is on and decreases during the period of time the switch off. Thevoltage V₃₀₂ across the diode in the first circuit is negative and isequal to the voltage of the electrochemical cell V_(load) because thediode 302 is blocking the flow of current through the electrochemicalcell. Thus, the current is being shunted through the first thyristorswitch 298 with the result that the current I₃₀₂ flowing through thediode is equal to the current I_(load) through the electrochemical cellis discontinuous. Thus, the inductor 300 in the boost regulator acts asan intermediate storage of electrical energy because the output voltageis greater than the input voltage. In the buck regulator the inductor100 acts as a filler to provide a continuous source of current to theelectrochemical cell. In summary, the buck regulator has a discontinuoussource of current resulting in a continuous output of current and in theboost regulator the source of current is continuous and the outputcurrent is discontinuous. This continuous current may be a source of ACripple in the electrolysis cell by placing a plurality of boostregulators in parallel, this effect will be decreased.

The second commutation circuit in the boost regulator and the buckregulator work the same in both circuits. In both circuits you gate thecommutation thyristor 116,316 by producing a pulse of current Q₂ frommicrocomputer. As a result of the discharge of the capacitor 120,320 andthe re-recharging of the capacitor with reverse polarity, a buck currentflows and forces the current through the switch thyristor 98, 298 tozero with the excess current flowing back into the capacitor and therest going to replace the output current of the thyristor. Thus, thecommutation circuits are the same in both the buck regulator and theboost regulator.

FIG. 5 and 7 shows an improved design of the buck regulator and theboost regulator includes the two improvements mentioned earlier. Thefirst improvement is a resistor for the current to charge the capacitor120,320. This enables an operator to be sure that sufficient chargeexists on the capacitor for the capacitor to provide a source of currentfor commutation. In cases where the resistor is not employed as is shownin the basic design of the buck regulator in FIG. 4, the microcomputermight be programmed to supply an initial charge to the capacitor toensure that a sufficient charge on the capacitor exists during start-upoperation. As will be realized, the conern for the intial charge on thecapacitor is a concern during start-up operations but is not once eitherregulator is running.

The second improvement to both the buck regulator and the boostregulator is replacing the diode 118,318 in the commutation circuit witha thyristor 118,318. In both the buck regulator and the boost regulatorshown in FIG. 5 and FIG. 7, the control signal Q₂ causes the capacitorto ring and charge before it can discharge into the diode. Thus, beforeyou actually turn the current off through the switch thyristor 98,298,you must wait for the capacitor to charge. By replacing the diode with asecond thyristor 128,328 in you can initial the charging action earlier,in fact right after the signal Q₁, have the capacitor already charged sothat it waits for a gate signal Q₃ to the third thyristor. As soon asthe gate signal Q₃ reaches the thyristor Q₃, the thyristor dischargesthe capacitor and it enables you to save, for example, a hundredmicroseconds resulting in a finer control of the current through thedirect current converter. If only a diode D₂ is in the circuit, than assoon as the capacitor reverses its polarity and reaches a full chargethe capacitor will discharge through the diode.

As will be realized the direct current converter may consist of aplurality of boost regulators or buck regulators extending in parallelwith each other between the fuel cell and the electrochemical cells.This will result in reduced probability for AC ripple in theelectochemical cell when using a boost regulator. As will beappreciated, AC ripple is to be avoided if possible in electrochemicalcells.

Although the invention has been shown and described with respect todetailed embodiments thereof, it should be understood by those skilledin the the art that various changes in form and detail thereof may bemade without departing from the spirit and the scope of the claimedinvention.

We claim:
 1. An apparatus for carrying out an electrochemical processwhich comprises:a chlorate electrolysis cell which uses input electricalpower at a first voltage and a first current to produce a chlorateproduct and hydrogen; at least one fuel cell which utilizes hydrogen toproduce output electrical power at a second voltage which is independentof the voltage of the electrochemical cell and a second current; meansfor supplying the hydrogen produced by the electrolysis cell to the fuelcell for comsumption of at least a portion of the hydrogen by the fuelcell; and, regulator means responsive to the power produced by the fuelcell and responsive to the hydrogen available to the fuel cell forsupplying output power received from the fuel cell as input power at thefirst voltage to the electrolysis cell, said means being electricallyconnected to the fuel cell and the electrolysis cell and said meansemploying gated switch means which intermittently passes current forregulating the electrical power received from the fuel cell to adjustthe current and voltage supplied by the fuel cell so that the voltagechange across said regulator means is equal to the difference betweenthe first voltage and the second voltage.
 2. The apparatus as claimed inclaim 1 wherein the electrolysis cell is a first source of hydrogen andwherein the apparatus includes a second source of hydrogen for supplyingadditional hydrogen to the fuel cell.
 3. The apparatus as claimed inclaim 1 wherein the fuel cell supplies a portion of the power to theelectricalchemical cell and wherein the apparatus further includes meansfor supplying additional power to the electrolysis cell.
 4. Theapparatus as claimed in claim 3 wherein the fuel cell has a schedule ofdesired operating voltages and wherein the fuel cell includes a meansfor controlling the fuel cell voltage such that the voltage of the fuelcell lies within said schedule of desired operating voltages.
 5. Theapparatus as claimed in claim 4 wherein said gated switch meansresponsive to a gate signal which has a conducting position and anonconducting position and wherein said regulator means includes aninductor connected to said gated switch means for resisting changes incurrent through the inductor and generating a voltage change across theinductor, wherein said regulator means includes pulse means for creatinga current pulse to deenergize said gated switch means, said pulse meansbeing connected to the gated switch means at a point between the gatedswitch means and the inductor, and includes means to enable the flow ofcurrent to the electrolysis cell during the period of time said switchis in the nonconducting position through said inductor and to oppose thediversion of the flow of current from the electrolysis cell to groundthrough a point between said gated switch means and said inductor. 6.The apparatus as claimed in claim 5 wherein the gated switch means is afirst gated switch means and wherein said pulse means includes a secondgated switch means responsive to a second gate signal and a means fordeveloping a current pulse which is in series with said second gatedswitch means, wherein said second gated switch means passes a current tothe means for developing a current pulse in response to a gate signal.7. The invention as claimed in claim 6 wherein said means for developinga current pulse includes a capacitor for storing charge and furtherincludes a third gated switch means responsive to a third gate signalwhich is connected to the capacitor and the first gated switch means,wherein the third gated switch means conducts the current pulse to thefirst gated switch as the capacitor discharges through the third gatedswitch means.
 8. The invention as claimed in claim 7 wherein saidregulator means is a bucking regulator having a first circuit and asecond circuit, the first circuit having a first leg extending betweenthe fuel cell and the electrolysis cell and a second leg extendingbetween the fuel cell and the electrolysis cell, wherein the first legincludessaid first gated switch, wherein said first gated switch is afirst thyristor having an anode and a cathode, said inductor wherein theinductor is connected to the cathode of the first thyristor and inseries with the first thyristor between the first thyristor and theelectrolysis cell, and said means to enable the flow of current to theelectrolysis cell, wherein said means to enable the flow of current is asecond diode having a cathode and an anode, the diode being connected toa point between the first thyristor and the inductor in the first leg,the diode being connected to the second leg such that the cathode of thesecond diode is joined to the cathode of the first thyristor;wherein thesecond circuit includes the pulse means for creating a current, thesecond circuit including a first leg having a first parallel diodeextending in parallel across the first thyristor of the first circuit,the anode of the parallel diode being connected to the cathode of thefirst thyristor for conducting a portion of the current pulse to saidcapacitor, a second leg extending in parallel across the firstthyristor, the second leg having said second gated switch means, saidsecond switch means being a second thyristor in series with said thirdgated switch means, wherein the cathode side of the third switch meansis connected to the cathode side of the first thyristor and the anodeside of the second thyristor being connected to the anode side of thefirst thyristor, and a third leg connected in parallel from the anodeside of the first thyristor to the cathode side of the second thyristor,the third leg including said capacitor and a second inductor, thecapacitor having one side connected to the anode side of the firstthyristor and a second side connectec to the inductor and through theinductor to the cathode side of the second thyristor.
 9. The inventionas claimed in claim 8 wherein a resistor extends from a point betweenthe capacitor and the second inductor in the third leg of the secondcircuit to the second leg of the first circuit.